Speaker can be seen in a surveillance video starting a casual conversation with Ahmed before pulling out a gun, pointing it at Ahmed, and demanding money. Ahmed followed Speaker's orders immediately and gave him cash without a fight.

Speaker, 18, of Eureka, then shot Ahmed anyway.

He shot him in the chest at point-blank range.

After Speaker admitted guilt to all charges against him Friday, defense attorney Jesse Ruben said he will leave it up to his client to explain his actions.

"I'm going to leave that to Christian to explain. I would tell you that the reasons are not particularly...They're more sad than anything," Ruben said.

The teenager's plea carries a minimum mandatory sentence of 50 years to life in prison. He is scheduled to be sentenced June 20.

"Mr. Speaker had gotten everything he needed and he decided to kill that man," prosecutor Alex Byers said. "It was awful and senseless. There was no point in that. It's hard to imagine people who are capable of doing such things."